1. Field of the Invention
This invention relates to an electric discharge lamp lighting device suitably applied to lighting of a plurality of electric discharge lamps used as a back light source of a liquid crystal display available for a liquid crystal television, a personal computer, a word processor or the like. More particularly, the present invention is concerned with an electric discharge lamp lighting device, which permits a liquid crystal display screen to be free from flicker.
2. Description of the Prior Art
An electric discharge lamp lighting device as one of the prior arts for lighting of a plurality of electric discharge lamps is configured as shown in FIG. 7. In this case, inverter circuits 20 are connected in parallel to a DC power source 2, and an electric discharge lamp 1 is provided on the output side of each inverter circuit 20.
In an electric discharge lamp lighting device of a type using a synchronous circuit, an inverter transformer needs a tertiary winding making no connection to the base side of a transistor, as disclosed in Japanese Patent Laid-open No. 2000-12255, for instance.
Since the electric discharge lamp lighting device as shown in FIG. 7 in the above prior art needs the plurality of parallel-arranged inverter circuits for lighting of a large number of electric discharge lamps, oscillations at different frequencies occur depending on variations in fixed number of components required for each inverter circuit and a difference in loading state. Thus, there is a problem of flicker of the electric discharge lamps, resulting in flicker of a liquid crystal display screen.
A problem with the electric discharge lamp lighting device of the type using the synchronous circuit is that it is not possible to use the synchronous circuit unless the inverter transformer has the tertiary winding making no connection to the base side of the transistor.
In view of the above circumstances, it is an object of the present invention to provide an electric discharge lamp lighting device, which permits synchronization of oscillation frequencies of inverter circuits to eliminate flicker from electric discharge lamps, in its turn, flicker from a liquid crystal display screen by connecting a primary winding of each separately-provided synchronization transformer in parallel between collectors of a pair of transistors of the electric discharge lamp lighting device including a resonance-type Royer""s inverter circuit as one of components, while connecting secondary windings of the synchronization transformers in parallel to each other.
For achieving the above object, according to the present invention as defined in claim 1, there is provided an electric discharge lamp lighting device comprising an inverter circuit, which uses a DC power source as input, and is configured that a primary winding having an intermediate tap of an inverter transformer, a resonance capacitor and a primary winding of a synchronization transformer are connected together in parallel between collectors of a pair of transistors, an electric discharge lamp is connected in parallel to a secondary winding of the inverter transformer to supply discharge power to the electric discharge lamp, the opposite terminals of a tertiary winding of the inverter transformer are connected to the bases of the transistors respectively for switching operation of the transistors by application of feedback voltage from the tertiary winding of the inverter transformer, and a secondary winding is provided for the synchronization transformer. The inverter circuit is provided every electric discharge lamp, and the secondary winding of the synchronization transformer of one inverter circuit is connected in parallel to the secondary winding of the synchronization transformer of, the other inverter circuit for synchronization of oscillation frequencies of a plurality of inverter circuits.
An electric discharge lamp lighting device according to the present invention as defined in claim 2 is characterized in that one terminal of the secondary winding of the above synchronization transformer is connected in parallel to the secondary winding of the synchronization transformer of the other inverter circuit through a switch. Thus, independent DUTY dimming and lighting-off of the electric discharge lamp are permitted without the need for synchronization of only a desired inverter circuit.
An electric discharge lamp lighting device according to the present invention as defined in claim 3 is characterized in that one terminal of the secondary winding of the above synchronization transformer is grounded. Thus, the circuit configuration is simplified to facilitate manufacture of a substrate.
An electric discharge lamp lighting device according to the present invention as defined in claim 4 is characterized in that one terminal of the secondary winding of the above synchronization transformer is grounded through a switch. Thus, only a desired inverter circuit may be disconnected from synchronization, and besides, the circuit configuration is simplified.
An electric discharge lamp lighting device according to the present invention as defined in claim 5 is characterized in that one terminal of the secondary winding of each synchronization transformer is grounded through a rectifying circuit and a switch, and the other terminal of the secondary winding of each synchronization transformer is made connection while being grounded through an element having an inductance component.
An electric discharge lamp lighting device according to the present invention as defined in claim 6 is characterized in that one terminal of the secondary winding of each synchronization transformer is grounded, and the other terminal of the secondary winding of each synchronization transformer is made connection while being grounded through an element having an inductance component.